1. Field of the Invention
The present invention relates generally to the construction and use of vascular catheters. More particularly, the present invention relates to a vascular catheter which provides both ultrasonic imaging capability and an optical system for delivering laser energy within the field of view of the imaging capability.
Arteriosclerosis is a pandemic health problem which can cause myocardial infarction (heart attack) and a variety of other circulatory diseases. Arteriosclerosis is characterized by vascular constrictions, generally referred to as stenoses, which result from the formation of atheroma on the interior wall of the blood vessel. Initially, atheroma is soft and has a relatively low density. Over time, however, the atheroma calcifies into a hard plaque having a high density which can significantly occlude a blood vessel. Moreover, once plaque forms, platelets can aggregate on the diseased blood vessel wall, further occluding the lumen.
Numerous approaches for reducing and removing such vascular obstructions have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of stenosis, atherectomy where a blade or cutting bit is used to sever and remove the obstruction, and laser angioplasty where laser energy is used to ablate at least a portion of the obstruction.
Each of these approaches finds use under different circumstances. For example, laser angioplasty is well suited for penetrating severe occlusions which leave little or no room for entry of balloon or atherectomy catheters. By utilizing appropriate wavelengths, laser energy can be used to penetrate even the most refractory stenoses. Frequently, laser angioplasty is utilized to create a passage through a severe occlusion, and the resulting passage utilized for subsequent balloon angioplasty or blade atherectomy to debulk or widen the lumen. Laser angioplasty is advantageous in that it generally results in the ablation of the occluding material, minimizing the release of emboli and other particulates which can cause secondary circulatory problems.
Despite its advantages, laser angioplasty suffers from numerous drawbacks. In particular, because of the high penetrating power, misdirection of the laser beam can cause penetration and piercing of the blood vessel wall. This problem arises because of the difficulty in positioning and aiming a laser catheter within a blood vessel. Generally, such positioning and aiming is accomplished by fluoroscopy which yields little information concerning the position of the cell wall, the precise direction in which the laser is aimed, and the nature of the obstructing material. The latter information is important because hardened plaque will generally require more energy to penetrate than relatively soft plaque or thrombus.
To overcome these problems, it has been proposed to combine laser angioplasty with various viewing systems. Most commonly, laser catheters have been provided with optical viewing systems employing optical waveguides which run in parallel with the waveguides carrying the laser energy. Such systems, however, are problematic in that they require stoppage of blood flow and flushing of the blood vessel with a clear liquid such as saline in order to allow viewing. Moreover, optical systems provide little or no information concerning the amount and distribution of plaque in the arterial wall.
To partially overcome these limitations, the use of ultrasonic imaging sensors with laser catheters has been proposed. In particular, a fixed ultrasonic transducer has been placed at the distal end of a catheter tube with an optical waveguide terminating at its center. The optical waveguide is coupled to a laser energy source and generally directs laser energy in the direction of viewing. The system, however, is limited to generally forward viewing and laser ablation, and is not particularly useful in debulking or widening the arterial lumen.
In addition to aiming difficulties, laser catheters generally have a very narrow field of penetration and have not been particularly useful in widening blockages in the blood vessel lumen. While some provisions have been made for deflecting a laser beam laterally to remove plaque and thrombus from the blood vessel wall, without precise information on the thickness of the stenosis, the chance of piercing the blood vessel is greatly increased.
For these reasons, it would be desirable to provide laser catheters having improved imaging capability. In particular, it would be desirable to provide laser catheters having an ultrasonic imaging capability which can be used to scan a relatively wide path around the blood vessel wall. Such systems should allow for precise aiming and control of the laser energy in order to provide for maximum penetration and ablation without damaging the blood vessel wall. Such systems should be useful for widening the central lumen in a radial direction as well as penetrating the lumen axially.
2. Description of the Background Art
Vascular catheters carrying fiber optics waveguides to deliver laser energy to stenosed regions within a blood vessel are known. U.S. Pat. No. 4,686,979, discloses a waveguide which is coupled to an excimer laser for performing laser angioplasty. U.S. Pat. No. 4,418,688, discloses a catheter having a waveguide carrying fiber optics for both viewing and delivery of laser energy, where the distal tip of the waveguide is deflectable to allow selective direction of the laser energy. WO 83/01893 (PCT US82/01669) also describes a vascular catheter which carries fiber optics for both viewing and laser ablation. U.S. Pat. No. 4,445,892, describes a vascular catheter having a rotatable axial waveguide with a mirror or prism at its end for allowing transverse viewing and transverse deflection of laser energy. U.S. Pat. No. 4,576,177, describes a vascular catheter including an optical fiber for delivering laser energy and a fixed ultrasonic transducer at the forward end for imaging an obstruction. A lens at the forward end of the optical fiber aligns the laser energy with the viewing direction of the transducer. U.S. Pat. No. 4,587,972 discloses a vascular catheter having a fiber optic bundle extending its length. A piezoelectric coating on the fibers at their distal end can generate axially directed ultrasonic energy in order to produce a longitudinal cross-sectional image. U.S. Pat. No. 3,938,502, describes an esophageal catheter having a plurality of radially-spaced ultrasonic transducers at its distal end. The transducers are utilized to obtain a complete cross-sectional view of the organ surrounding the catheter. French Patent Publication No. 78-14494 describes an esophageal catheter having an ultrasonic catheter rotatably mounted in a balloon. The transducer may be turned to direct the ultrasonic energy in a desired direction. European patent application 163 502 describes an atherectomy device using an axially translatable, rotating blade.
U.S. Pat. No. 4,794,931 and copending application Ser. No. 07/290,533, each describe a vascular catheter which combines an ultrasonic imaging capability with an atherectomy blade for severing stenosis from the vascular wall. The entire disclosures of both the patent and the application is incorporated herein by reference.